This invention relates to gas generators used with vehicle occupant safety devices, including without limitation, seat belt pretensioners, airbags, compressed gas vessel openers, and other devices requiring a rapid pulse of high-pressure gas.
Gas generators are used to inflate airbags. They can also be used to open vessels containing pressurized gas, and to tighten seat belts. More specifically, small xe2x80x9cgas generatorsxe2x80x9d are utilized with seat belt pretensioners and as a means to open vessels containing compressed gas. In a vehicle occupant restraint system an electrical current that is initiated by a crash sensor activates a gas generator. Generally, when the electrical current is received by an igniter housed within the gas generator, the ignition train is triggered resulting in ignition of the gas generant. The combustion of the gas generant produces hot gas at elevated pressures.
When a gas generator used with a seat belt pretensioner is activated, hot gas and resulting high pressure produced by combustion of the gas generant forces a piston or similar device with an attached cable to travel down a tube and remove excess slack in a seat belt. Other pretensioners employ a gas. generator to power a reel or ratchet to remove excess slack in the seat belt. Removal of slack in a seat belt is required to properly position a vehicle occupant during a crash by securing the vehicle occupant against the seat.
In a compressed gas vessel opener, the gases exiting the gas generator can be used to drive an object or place thermal or mechanical stress on a burst disk or diaphragm, resulting in punctures or general failure of the diaphragm or burst disk. Rupture or failure of the diaphragm/burst disk allows the compressed gas to escape.
Gas generators comprise igniters, which in general have a glass to metal hermetic seal or a plastic hermetic seal protecting the ignition charge material from moisture. The igniter body may have an overmold comprising a polymeric material. The overmold allows the igniter to form a seal against the gas generator as disclosed in U.S. Pat. No. 6,167,808.
The present invention relates to a gas generator that has a body or housing made entirely of a polymeric material. A polymeric gas generator body must withstand high temperatures and pressure encountered during ignition and combustion of the gas generant contained in the generator body. Another problem is related to the brisance properties of the gas generant. Brisance is a measure of a material""s ability to shatter. In a plastic or polymeric gas generator, the gas generant must be of the xe2x80x9clow brisancexe2x80x9d type and have soft ignition and combustion properties. A gas generant of this type is described in U.S. Pat. No. 6,071,364, and it functions well in plastic gas generators. U.S. Pat. No. 6,073,963 describes an injection-molded initiator with an injection molded insert member and teaches the need for an insert member. The present invention uses no such member. Instead the entire body and polymeric end cap comprise an injection-molded plastic and form a polymeric combustion chamber that houses a gas generant. The plastic gas generator of this invention is low cost, easily assembled, light weight, and made by injection molding, or similar technology.
A gas generator according to one aspect of the present invention has a polymeric end cap and an igniter subassembly comprising an igniter and a polymeric gas generator body. The gas generator body and the end cap define a hermetically sealed combustion chamber for receiving a gas generant. The igniter receives an electrical current and ignites a gas generant. The gas generator can be attached, mounted or retained by modifying or altering the external geometry to accommodate various designs.